1. Field of the Invention
The present invention relates to a method for producing polymer particles in a compressive fluid through heterogeneous polymerization of a ring-opening polymerizable monomer or through polymerization of an addition polymerizable monomer; and to polymer particles obtained by the method.
2. Description of the Related Art
Well known are methods of producing fine polymer particles through heterogeneous polymerization of a monomer in supercritical carbon dioxide, including emulsion polymerization, dispersion polymerization and suspension polymerization.
Heterogeneous polymerization in supercritical carbon dioxide has the following advantages over heterogeneous polymerization in water or organic solvents, and thus is utilized as a method for producing fine polymer particles from various monomers. The obtained polymer particles are used for various applications such as electrophotographic developers, printing inks, building paints and cosmetics. Specifically, the advantages are as follows.    (1) Solvent removal and drying after polymerization can be simplified.    (2) Treatment of waste solvent can be omitted.    (3) Highly toxic organic solvent is not needed.    (4) Residual unreacted monomer components and hazardous materials can be removed at a washing step.    (5) Used carbon dioxide can be recovered and recycled.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2009-167409 discloses a method of synthesizing colored polymer particles from a radical polymerizable monomer in the presence of a surfactant containing a perfluoroalkyl group. However, the fluorine-containing surfactant used in this method is very expensive and also is problematic in terms of safety. Further, this method cannot produce polymer particles having a small molecular weight distribution (Mw/Mn) (about 2 or smaller) attained by the present invention.
JP-A No. 2009-132878 discloses a method of producing polymer particles using a polymer radical polymerization initiator containing an organosiloxane skeleton, while synthesizing a polymer surfactant in one pot without separately synthesizing and preparing surfactants suitable for monomers. However, this method also cannot produce polymer particles having a molecular weight distribution (Mw/Mn) of 2 or less. Further, there is no description about ring-opening polymerizable monomers.
As described above, no reports have been presented on a method for producing polymer particles having a small molecular weight distribution with an inexpensive, highly safe means using a ring-opening polymerizable monomer or an addition polymerizable monomer in a compressive fluid such as a supercritical fluid.